Liquid-Crystalline Order in the Phosphorus-Containing DenDrimers.

The structure of phosphorus-containing dendrimers has been studied by IR spectroscopy and optical polarization microscopy. The repeating units of dendrimer molecules are mesogens. This property arises from the conjugation of the aromatic ring and the hydrazone group. An analysis of the IR spectra showed that, with an increase in the generation number, the width of the stretching vibration bands ν(PN) and ν(PO) increases. Difficulties in packing molecules of higher generations cause conformational diversity. The shape of the dendrimer molecules was determined by analyzing the increments of dipole moments. Additionally, the modeling of the stacking of repeating links was performed. The spherical model of molecules does not satisfy the experimental dipole moments of the dendrimers. The flat disk model is more suitable for explaining step changes in dipole moments. The liquid-crystalline ordering of dendrimers under the action of applied pressure was found. With simultaneous heating and uniaxial compression, optical anisotropy appears in dendrimers. It is associated with the formation of liquid-crystalline order. However, a thermodynamically stable liquid-crystalline phase is not formed in this case. Dendrimers most likely have disk-shaped molecules.

Study of the conformation and hydrogen bonds of the p-tetrasulfonatothiacalix[4]arene pentasodium salt by vibrational spectroscopy and DFT.

The vibrational spectra of the p-tetrasulfonatothiacalix[4]arene pentasodium salt (TCAS) and tert-butylthiacalix[4]arene (BuTCA) were studied. Comparison of the TCAS and BuTCA IR spectra allows us to isolate the bands of tert-butyl and sulfonate groups. Geometry, IR and Raman spectra were calculated for conformation cone, partial cone, 1,2-, and 1,3-alternate. The most stable conformation of the TCAS is the cone. Characteristic bands were determined for each of the possible conformations. In the case of the TCAS molecule, four ions of sodium are coordinated with the oxygen atoms of sulfonate groups, and the fifth ion interacts with the oxygen and sulfur atoms of the macrocycle. Under the influence of sodium ions, the distribution of electron density in the TCAS molecule and its ability to supramolecular interactions change.

Experimental and DFT investigation of structure and IR spectra of H-bonded associates of p-(3-carboxy-1-adamantyl)thiacalix[4]arene.

The IR spectra of p-(3-carboxy-1-adamantyl)thiacalix[4]arene (1-AdCOOHTC4A) have been studied. IR spectra of crystalline 1-AdCOOHTC4A obtained at room temperature or upon heating to 250 °C or its dilute solutions lack bands of free hydroxyl groups. The frequency of hydroxyl groups at 3377 cm-1 indicates the formation of an intramolecular H-bond along the lower rim of the 1-AdCOOHTC4A molecule. On the top edge of thiacalixarene, the carboxyl groups form dimeric or cyclic tetrameric complexes via intermolecular H-bonds. The conformation of the cone persists, but there is a mutual influence of H-bonds along the upper and lower rims of the thiacalix[4]arene molecule. The structure with dimer H-bonds between carboxyl groups is 31.9 KJ/mol less preferable than the conformation with tetramer cyclic H-bonds for 1-AdCOOHTC4A. Comparison of the absorption band of νOH alcohol hydroxyl groups in the IR spectra of 1-AdCOOHTC4A at 3377 cm-1, with the corresponding band of 1-AdTC4A at 3372 cm-1, suggests that the presence of the second system of H-bonds of carboxyl groups in the first molecule does not affect the H-bond of alcohol hydroxyl groups.

Liquid and back gate coupling effect: toward biosensing with lowest detection limit.

We employ noise spectroscopy and transconductance measurements to establish the optimal regimes of operation for our fabricated silicon nanowire field-effect transistors (Si NW FETs) sensors. A strong coupling between the liquid gate and back gate (the substrate) has been revealed and used for optimization of signal-to-noise ratio in subthreshold as well as above-threshold regimes. Increasing the sensitivity of Si NW FET sensors above the detection limit has been predicted and proven by direct experimental measurements.

IR and NMR spectra, intramolecular hydrogen bonding and conformations of para-tert-butyl-aminothiacalix[4]arene in solid state and chloroform solution.

It is demonstrated that dissolution of aminothiacalix[4]arene in chloroform results in transformation of 1,3-alternate conformation, adopted in single-crystal and bulk polycrystalline solids, to the pinched-cone form. This conformer is stabilised by the intramolecular hydrogen bonds of two distal amino-groups acting as H-donors with another two amino moieties that appear as H-acceptors. The H-bonds cause quite small (ca. 10-20 cm(-1)) red shift of the IR bands of the NH(2) stretching vibrations, which suggests rather weak NHcdots, three dots, centeredN hydrogen bonding. This latter is sufficient to stabilize the pinched-cone conformation in the chloroform solution, but the energy gap between the pinched-cone and other conformations is small, and solid-state intermolecular forces easily overcome it, leading to realisation of the 1,3-alternate conformer. The comparison of the DFT computed and experimental vibrational and NMR spectra demonstrates good quality of present quantum-chemical computations, allows complete interpretation of the spectra and reveals simple IR and NMR spectroscopic markers of the conformers of aminothiacalix[4]arenes.